From: Kees Cook <keescook@chromium.org>
To: Paul Moore <paul@paul-moore.com>
Cc: Oleg Nesterov <oleg@redhat.com>,
Casey Schaufler <casey@schaufler-ca.com>,
"chengjian (D)" <cj.chengjian@huawei.com>,
NeilBrown <neilb@suse.com>,
Anna Schumaker <Anna.Schumaker@netapp.com>,
Kees Cook <keescook@chromium.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
"Xiexiuqi (Xie XiuQi)" <xiexiuqi@huawei.com>,
Li Bin <huawei.libin@huawei.com>, Jason Yan <yanaijie@huawei.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Linux Security Module list
<linux-security-module@vger.kernel.org>,
SELinux <selinux@vger.kernel.org>
Subject: Re: kernel BUG at kernel/cred.c:434!
Date: Mon, 15 Apr 2019 22:40:52 -0500 [thread overview]
Message-ID: <CAGXu5jKYmoaR6bxW82ogN4iOeKi8AtEwkvVvCXd_gn3CCwFU2Q@mail.gmail.com> (raw)
In-Reply-To: <CAHC9VhSk1_fWooexHK0+5cKum55qTvj3uv5sRE=aJ4mv2GHJZg@mail.gmail.com>
On Mon, Apr 15, 2019 at 11:20 AM Paul Moore <paul@paul-moore.com> wrote:
>
> On Mon, Apr 15, 2019 at 11:05 AM Oleg Nesterov <oleg@redhat.com> wrote:
> > On 04/15, Paul Moore wrote:
> > >
> > > On Mon, Apr 15, 2019 at 9:43 AM Oleg Nesterov <oleg@redhat.com> wrote:
> > > > Well, acct("/proc/self/attr/current") doesn't look like a good idea, but I do
> > > > not know where should we put the additional check... And probably
> > > > "echo /proc/self/attr/current > /proc/sys/kernel/core_pattern" can hit the
> > > > same problem, do_coredump() does override_creds() too.
> > > >
> > > > May be just add
> > > >
> > > > if (current->cred != current->real_cred)
> > > > return -EACCES;
> > > >
> > > > into proc_pid_attr_write(), I dunno.
> > >
> > > Is the problem that do_acct_process() is calling override_creds() and
> > > the returned/old credentials are being freed before do_acct_process()
> > > can reinstall the creds via revert_creds()? Presumably because the
> > > process accounting is causing the credentials to be replaced?
> >
> > Afaics, the problem is that do_acct_process() does override_creds() and
> > then __kernel_write(). Which calls proc_pid_attr_write(), which in turn calls
> > selinux_setprocattr(), which does another prepare_creds() + commit_creds();
> > and commit_creds() hits
> >
> > BUG_ON(task->cred != old);
>
> Gotcha. In the process of looking at the backtrace I forgot about the
> BUG_ON() at the top of the oops message.
>
> I wonder what terrible things would happen if we changed the BUG_ON()
> in commit_creds to simple returning an error an error code to the
> caller. There is a warning/requirement in commit_creds() function
> header comment that it should always return 0.
Would callers be expected to call abort_creds() on failure? There are
a number of places where it'd need fixing up. And would likely be best
with a __must_check marking.
It seems like avoiding the pathological case might be simpler?
--
Kees Cook
next prev parent reply other threads:[~2019-04-16 3:41 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-12 6:21 kernel BUG at kernel/cred.c:434! chengjian (D)
2019-04-12 15:28 ` Casey Schaufler
2019-04-15 13:43 ` Oleg Nesterov
2019-04-15 14:48 ` Paul Moore
2019-04-15 15:05 ` Oleg Nesterov
2019-04-15 16:20 ` Paul Moore
2019-04-16 3:40 ` Kees Cook [this message]
2019-04-16 14:46 ` chengjian (D)
2019-04-17 14:30 ` Paul Moore
2019-04-17 14:57 ` Oleg Nesterov
2019-04-17 15:39 ` Casey Schaufler
2019-04-17 15:40 ` Paul Moore
2019-04-17 16:27 ` Oleg Nesterov
2019-04-17 16:42 ` Casey Schaufler
2019-04-18 13:39 ` Stephen Smalley
2019-04-17 23:39 ` Paul Moore
2019-04-18 0:17 ` John Johansen
2019-04-18 0:24 ` Casey Schaufler
2019-04-18 2:49 ` Yang Yingliang
2019-04-19 2:04 ` Paul Moore
2019-04-19 2:34 ` Yang Yingliang
2019-04-19 13:24 ` Paul Moore
2019-04-19 14:34 ` Yang Yingliang
2019-04-19 16:13 ` Paul Moore
2019-04-20 7:38 ` Yang Yingliang
2019-04-22 19:48 ` Paul Moore
2019-04-23 4:08 ` Yang Yingliang
2019-04-23 20:18 ` Paul Moore
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